1. Field of the Invention
The present invention relates to a projection-type liquid-crystal display device such as a light source device used in a projector, and particularly to a compact light source device suitable for use in a compact projector.
2. Description of the Related Art
In conventional practice, projectors in which images on liquid-crystal display elements are magnified, projected, and displayed are configured such that a single liquid-crystal display element is illuminated by a metal halide lamp from behind, and the image displayed by the liquid-crystal display element is magnified and projected by a projection lens.
For example, Japanese Unexamined Patent Applications (Kokai) 62-237485, 3-75737, and 8-111107 describe inventive structures in which a metal halide lamp or a halogen lamp are used as the light source, and light emitted by this light source is transmitted through a hollow light-guide structure and directed toward a liquid-crystal display element.
The above-described prior art, however, involves using a lamp as the light source, and is limited in the degree to which the size of the light source as such can be reduced. It is thus difficult to reduce the size of the projector as a whole. Portable communication terminal devices have appeared in recent years, dispensing with the need to project images to dimensions in excess of 60 inches with such projectors. It is proposed, for example, that the size of a projected image be reduced to about 10 or 20 inches. At this size of a projected image, a light-emitting element (light-emitting diode, semiconductor laser, etc.) or the like can be used as the light source, making it possible to design very small projectors.
Light-emitting elements and other miniature light-emitting devices are substantially point light sources, and it is therefore difficult to uniformly illuminate a liquid-crystal display element having a given surface area. An attempt to line up a plurality of light-emitting diodes and to illuminate a wide surface area ultimately yields an assembly of point light sources, resulting in a nonuniform distribution of light intensity in a two-dimensional plane.
Japanese Unexamined Patent Application 10-123512 discloses projector technology in which the light source is made up of a two-dimensional array of light-emitting diodes. Light from the light-emitting diodes is converted to planar light by microlens array (an array of lens elements formed in conformity with the light-emitting diodes) in order to allow light radiated by the light-emitting diodes (point light sources) to be directed toward liquid-crystal display elements in an efficient manner.
Such microlens arrays are disadvantageous, however, in that the lens action along the border between adjacent lens elements becomes weak as a result of manufacturing errors or the like, making it difficult to create uniform illumination light.
According to another arrangement, which is disclosed in Japanese Unexamined Patent Application 9-73807, the optical axis can be curved 90xc2x0 to guide the light, but a technique has yet to be found that would allow the optical axis of a point light source to advance in a straight line, yielding planar light.
An object of the present invention, which was perfected in view of the above-described situation, is to provide a light source structure in which a plurality of point light sources are arranged in a planar configuration and which is suitable for miniaturization. Another object of the present invention is to provide a compact light source capable of displaying projected images having uniform light intensity by designing a structure capable of emitting uniform light through the use of a plurality of light-emitting diodes or other point light sources for illumination purposes.
The present invention resides in a light source device comprising light guide means that is provided with mutually opposite end faces and that has a light guide function whereby light entering through one end face is guided to and emitted from the other end face, and a point light source array that is a separate entity from the light guide means and that is obtained by arranging a plurality of point light sources in a planar configuration along one of the end faces of the light guide means.
The present invention also resides in a light source device comprising the following separate entities: a point light source array obtained by arranging a plurality of point light sources in a planar configuration, and light guide means in which light from the point light source array is admitted through at least one end, mixed, guided to the other end face, and emitted.
As a result of thoroughgoing research aimed at miniaturizing light sources and concerned with the relation between light guide means and planar point light source arrays, the inventor discovered that the stated object can be attained by providing a rectilinear or serial arrangement for the surface through which light is admitted into the light guide means and the surface through which the light admitted into the light guide means is allowed to escape in relation to the point light sources, and by the uniform dispersion of light received from the point light sources throughout the light guide body.
Based on the above discovery, the present invention has the following distinctive features.
The present invention is characterized in that the aforementioned point light sources are light-emitting elements that emit monochromatic light. Such light-emitting elements include light-emitting diodes (hereinafter xe2x80x9cLEDsxe2x80x9d), semiconductor lasers (LDs), and other point light sources, and are not limited in terms of emitted color. In other words, monochromatic elements (for example, white LEDs or light-emitting diodes that emit B (blue) light) may also be used.
When B (blue) light or other monochromatic light is used, wavelength conversion elements for converting this light to white light should preferably be disposed in the optical path.
The present invention is also characterized in that the aforementioned point light sources are light-emitting elements that differ in color, and the aforementioned point light source array is a combination of such light-emitting elements.
Such a combination of light-emitting elements may be a combination of three colors (RGB), a combination that includes colors other than these three colors (for example, orange and yellow green), or a combination of two, four, or more colors.
The present invention is further characterized in that the aforementioned light guide means is a hollow or solid light guide body, preferably composed of a transparent material. A first aspect of this light guide body is a hollow light guide block, which may be polygonal prismatic or cylindrical in shape. Reflecting metal surfaces may also be provided to the lateral surfaces (inner wall surfaces and inner peripheral surfaces) of the hollow light guide block.
A second aspect of the light guide body is a solid (rather than hollow) light guide block. Total reflection surfaces or reflecting metal surfaces may also be provided to the lateral surfaces of the solid light guide block. The light guide body may also be configured as a so-called Selfoc lens, which is obtained by forming a bundle from a plurality of optical fibers having a cladding and a core.
Another aspect of the present invention is an optical device comprising the aforementioned light source device and a member located opposite the end face for emitting the light of the light guide means and designed to modulate the light from the light guide means. Yet another aspect of the present invention is a liquid-crystal display device characterized in that this member is a liquid-crystal display element. According to this embodiment of the liquid-crystal display device, a magnifying lens is disposed in the optical path of the emitted light optically modulated by the aforementioned liquid-crystal display element. It is also possible to provide a screen configured such that the image of the liquid-crystal display element can be projected by the magnifying lens.
By allowing light emitted by the end face of the light source device thus configured to strike the liquid-crystal display element, it is possible for the image displayed by the liquid-crystal display element to be viewed directly, in magnified form, or in projected form.
A distinctive feature of the present invention is that light guide means is provided such that the illumination light from the light source device preferably propagates in a straight line without bending its optical axis and that the entire surface area (region) necessary for displaying images is uniformly illuminated in the process, making it possible to efficiently illuminate the illumination region (an image display region in the case of a liquid-crystal display device) while preventing light from being scattered outside the illumination region.
The present invention resides in a light source device comprising a light guide block provided with an inner wall capable of reflecting light, and shaped as a hollow component to form a light guide; and a point light source array in which point light sources capable of emitting light into the light guide are arranged opposite an end face of the light guide block.
In this structure, light emitted by point light sources located near the center of the point light source array is emitted by the other end face of the light guide without being reflected by the inner walls of the light guide block. Light emitted by point light sources located near the periphery of the point light source array is reflected by the inner walls of the light guide block and is emitted by the other end face. Light emitted by such point light sources along various routes is uniformly mixed inside the light guide. Adjusting the length of the light guide in the direction of the optical axis provides uniform light intensity across the light emission surface of the light guide.
In this case, the aforementioned point light sources may, for example, be light-emitting diodes. In addition, the aforementioned light guide block may, for example, have a polygonal prismatic shape whose inner walls are composed of a plurality of flat reflecting surfaces. The aforementioned light guide block may also have a cylindrical or elliptical shape whose inner walls are composed of curved surfaces.
In the present invention, the term xe2x80x9can end face of a hollow light guide blockxe2x80x9d refers to the surface that corresponds to an end face of a solid block equivalent to the aforementioned hollow block.
The present invention is also a liquid-crystal display device that is provided with the aforementioned light source device, wherein this liquid-crystal display device further comprises a liquid-crystal display element located opposite the other end face of the light guide block and configured to allow light emitted by a light guide to be modulated, so that images can be viewed directly from the light emission side of the liquid-crystal display element. This structure may, for example, be applied to liquid-crystal display devices used in portable information equipment.
The present invention is also a liquid-crystal display device that is provided with the light source device of the present invention, wherein this liquid-crystal display device further comprises a liquid-crystal display element disposed facing the other end face of the light guide block and configured such that light emitted by a light guide can be modulated, and a magnifying lens disposed in the optical path of the emitted light optically modulated by the liquid-crystal display element. This structure may, for example, be used in a head-mounted display in which the image on the liquid-crystal display element can be viewed directly through a lens.
The present invention may also comprise a screen configured such that the image on the aforementioned liquid-crystal display element can be projected by a magnifying lens. This structure may be used in projectors or the like.
The present invention is also a liquid-crystal display device equipped with the light source device of the present invention, wherein this liquid-crystal display device further comprises a dichroic prism or other color synthesis means which comprise, in accordance with each primary color, prescribed color modulation units comprising light source devices so configured as to be able to emit light within the wavelength region of each primary color, and liquid-crystal display elements that are disposed facing the other end face of the light guide means and that are configured such that light emitted by the light guide can be modulated, and in which light emitted by the prescribed color modulation units can be synthesized; and a projection lens disposed in the optical path of the emitted light synthesized by the color synthesis means.
The present invention is also a liquid-crystal display device equipped with the light source device of the present invention, wherein this liquid-crystal display device further comprises a dichroic prism which comprises, in accordance with each primary color, prescribed color modulation units comprising light source devices capable of emitting white light, liquid-crystal display elements that are disposed facing the other end face of the light guide means and that are configured such that light emitted by the light guide can be modulated, and filters so configured as to be able to transmit light within the wavelength region of each primary color, and in which light emitted by the prescribed color modulation units can be synthesized; and a projection lens disposed in the optical path of the emitted light synthesized by the dichroic prism.
The present invention is also a light source device comprising a flat light source array forming a planar configuration from a plurality of light-emitting elements for emitting light of the three primary colors, and a light guide body composed of a transparent material in which incident light from the flat light source array is guided to the emission side.
The present invention is also a light source device comprising a flat light source array obtained by forming a planar configuration from a plurality of light-emitting elements for emitting monochromatic light, and a light guide body composed of a transparent material in which incident light from the flat light source array is guided to the emission side; further comprising a luminescent film located opposite the light-receiving surface or light-emitting surface of the light guide body and designed to convert the monochromatic light to white light.
The light source device comprises a circuit for the simultaneous or sequential lighting of the light-emitting elements for emitting light of each color. Another distinctive feature is that the light-emitting elements are light-emitting diodes.
The present invention is a liquid-crystal display device, comprising the aforementioned light source device; a liquid-crystal display element located opposite the light-emitting surface of the aforementioned light guide body; and a projection lens located on the opposite side from the light guide body with respect to the liquid-crystal display element. According to another aspect of the liquid-crystal display device pertaining to the present invention, liquid-crystal display elements are synchronized with the sequential lighting of the aforementioned light-emitting diodes, and images are sequentially formed based on video signals separated by color. In this case, white light is preferred for the aforementioned light-emitting diodes. Mixing of white LEDs or color-emitting LEDs (RGB) can be suggested as an embodiment involving emission of white light. When monochromatic (for example, blue) light-emitting diodes are used, a luminescent film in which monochromatic light emitted by the aforementioned light-emitting diodes is converted to white light should be placed opposite the light-receiving surface or light-emitting surface of the aforementioned light guide body.
The aforementioned light-emitting diodes are light source devices composed of a plurality of colors based on the three primary colors and lighted simultaneously or sequentially, each producing white light. The formation of after images in the human eye is used when sequential lighting is employed.
According to another aspect of the liquid-crystal display device pertaining to the present invention, the aforementioned light-emitting diodes are composed of a plurality of colors based on the three primary colors, these diodes are sequentially lighted, the aforementioned liquid-crystal display elements are synchronized with the sequential lighting of the aforementioned light-emitting diodes, and images are sequentially formed based on video signals separated by color. High resolution can be obtained because images can be displayed for each color. In this case as well, color images can be obtained due to the existence of after images.
As referred herein, the term xe2x80x9clight guide meansxe2x80x9d denotes a functional means for guiding light from a light source. An embodiment of such a light guide means is a light guide body serving as a member for realizing this light guiding function. An embodiment of such a light guide body is a light guide block. The light guide body may be a hollow or solid member. When the light guide body is a hollow component, the internal surfaces thereof should preferably be provided with reflecting metal films, which are means capable of total light reflection, as described above.
This light guide body is shaped and dimensioned to allow light to be uniformly mixed. In addition, the spacing pitch and other characteristics of the point light sources constituting the point light source array should be adjusted such that light can be uniformly mixed in the light guide body.